1. Field of the Invention
This invention relates to a color image input apparatus or scanner which is used in a color copying machine and the like. The invention particularly relates to a color image input apparatus which inputs a color image by plural CCDs which are installed in parallel.
2. Discussion of the Background
Conventionally, there is an apparatus which is shown in FIG. 5 as a color image input apparatus. That is, three CCDs 501R, 501G, 501B which corresponded to R, G, B respectively are installed in some interval (8 lines in FIG. 5) in the sub-scanning direction in parallel. The three line CCDs 501 resolve a color image into image pixel data of R, G, B which corresponded to the CCDs, 501R, 501G, 501B. In this apparatus, the three line CCDs 501 move in a sub-scanning direction, relative to a document being scanned, in the order of B, G, R and are installed at 8 line intervals respectively. Therefore, the CCD 501B reads at a given position of a document image, the CCD 501R reads at position which is delayed 8 lines and the CCD 501R reads the position at a delay of 16 lines. B pixel data which is read by the CCD 501B is output at a delay of 16 lines, G pixel data which is read by the CCD 501G is outputted at a delay of 8 lines, and R pixel data which is read by the CCD 501R is output at real time. As a result, the document image in the position can be obtained as R, G, B pixel data.
According to the above technique, the time difference of line unit in the sub-direction is corrected by a delay process and therefore the R, G, B pixel data of the same line of the document image can be obtained. However, it is assumed that the three CCDs read the image of the same position in the main scanning direction, and the different of the reading position in the main direction is not considered. Therefore, a problem of a color difference by the difference of the reading position in the main direction occurs. Specifically, as shown in FIG. 6, the difference of the reading position in the main direction by the twist of the three line CCDs and the distortion when they are installed (.DELTA.x in FIG. 6) and the like may occur. As a result, the problem of a color difference occurs and a clear image cannot be obtained.